Infertility and Action of the Gene for Rose Comb in the Domestic Fowl

I t has been rcported that the poor reproductive ability of White Wyandotte domestic fowl is due to very low fertility of homozygous rose co111b males (Crawford and Merritt, 1963; Crawford and Sn~yth , 1961a). Rose comb, deterillined by a conlpletely dominant autosonla1 gene R, is characteristic of the Wyandotte breed although single comb, determined by the recessive allele r, occurs frequently. Embryo mortality might still be found to be the real cause of the deficient reproduction, since mortality occurring early in the preoviposital period would not have been detected by the techniques that were used to measure fertility (Crawford and Smyth, 1964a). I t is also possible that the problem arises prior to fertilization through selective reduction in viability of male gametes. These situations inight be indicated by abnormal ratios among the progeny. Comparisons of the sex and comb type ratios of offspring obtained froin matings involving males of the three comb genotypes of interest (RR, Rr, and rr) will be presented in this report. In addition, a discussion will be presented concerning whether effects associated with the rose comb trait are due to linkage or to pleiotropy.